that series will begin saturday in san francisco. >>> authorities have dropped the preliminary investigation into another rape case involving former imf chair dominique straws kahn. we're looking at him during the 2011 rape scandal that forced him to step down from the imf. that's when a maid in a new york hotel falsely accused him of sexual assault. the charges were later dropped. >>> right now president obama and his republican rival are preparing for tomorrow night's first presidential debate. the outcome the debates could help decide the election. tara mergener reports that both campaigns are downplaying expectations. >> reporter: workers are setting the stage for wednesday night's presidential debate at the university of denver. both candidates are behind closed doors today getting ready. mitt romney is preparing in colorado and the latest polls show he is trailing the president in most swing states. >> we can do this. >> reporter: his running mate paul ryan is on a bus tour working to sway voters in iowa. >> our goal is to earn your support. we want to deserve this victory. >> reporter